For a variety of purposes, it is frequently desirable to treat articles, e.g. solid objects usually of metal, with solvents, solvent-containing liquid or solvent vapors and such treatments can involve degreasing with solvent liquids or solvent water, phosphorization of a metal surface and lacquering or lacquer coating of objects using a liquid containing a solvent.
It is known to provide apparatus for such purposes which includes an upwardly open treatment chamber, means for raising and lowering the articles in the chamber, e.g. to immerse the articles in the liquids and remove the articles from the liquid, a heater generally at the bottom of the chamber for vaporizing solvent, and cooling and condensing means in the region of the open treatment chamber edge, i.e. above the liquid bath to condense solvent vapors.
The apparatus can include a basket in which the articles are raised and lowered. The articles can be lowered into the liquid or raised therefrom or held in contact with vapor. An apparatus of this kind is described in German patent document No. 26 24 345, a heat pump being provided in this system, with its hot branch connected to the heater and its cold branch connected to the condenser.
In this system, the solvent of the liquid also forms a heat carrier or working medium of the heat pump.
The condensing means serves to condense vapors as they rise upwardly from the solvent-containing liquid so that a minimum of solvent escapes from the vessel.
The solvent content of the air in the region of the condenser and above the chamber is, of course, dependent upon the water pressure of the solvent at the temperature of the condenser. The lower the temperature which can be sustained at the condenser surface, the greater will be the recovery of solvent for the vapor phase and thus the escape of solvent into the environment from the treating vessel can be reduced by lowering the temperature of the condenser surface. However, in conventional systems there are practical limits to the temperature to which the condenser surfaces can be lowered and hence to the recovery of solvent vapors from the water phase so that hoods and other means for evacuating these vapors must be provided to minimize environmental pollution.